Hello Saheed,
I'd say since you've been away from your assignment a long while, I'd say
you should start all over again - It's very much worth the effort, you would have a clean design and it will be fresh in your head for the essay exam (2004 is a long time.)
If however you are not interested in starting all over again and you have tests (say
JUnit tests) written for your classes, you can go ahead and refactor then
test them. Andrew's book is a good one, so you're good to go.
All the best.